Metallization of various substrates, particularly silicon, with aluminum-based metals such as aluminum, Al-Si alloys, Al-Cu-Si alloys, and the like is commonplace in the manufacture of integrated circuits. Such metallizations are typically deposited in magnetron sputtering systems. Because aluminum is a reactive metal, impurity atoms and molecules in the vacuum chamber, particularly oxygen and water vapor, tend to react with and become part of the growing film. Even small concentrations of such impurities can influence properties of the film such as grain size, hardness, stress, resistivity and the like. Changes in these properties can, in turn, affect film adhesion to the substrate, etchability, contact resistance to device silicon, bondability and the like. Significant changes in these and other functional characteristics have frequently been noted in such films although there was no discernible change in the deposition conditions.
For example, an air leak of 10.sup.-3 torr-liters per second might cause a slight increase in pumpdown time, but would not prevent the chamber from reaching a base pressure of 10.sup.-6 torr. Throttling and backfilling with argon would immediately swamp out this pressure. However, such an air leak would result in an oxygen content of about one percent in an aluminum film, causing significant changes in film properties.
A wafer substrate for such metal depositions is usually covered by an oxide layer in which there are numerous small holes which expose the underlying silicon. The exposed silicon must have good contact, i.e. low resistance, with the overlying metallization in order for the circuit to function properly. This requires that the contact holes be well etched, the silicon surface be clean and the vacuum system be free of leaks and relatively free of impurities.
In the manufacture of large scale integrated circuits (LSICs) and very large scale integrated circuits (VLSICs), the metal deposition step is one of the last in the fabrication process sequence. Therefore, a considerable loss, both in time and material, will be incurred if metal deposition is not carried out properly.
Presently, contact integrity is tested only after the metal coating has been patterned and alloyed to improve the metal-to-silicon contact. Once patterning and alloying have been carried out, it is virtually impossible to strip the metal and repeat the metallization procedure. Therefore, when the conventionally used test shows poor metallization, a wafer lot must be discarded. In accordance with this invention, there is provided a means of accurately determining the contact resistance distribution of the aluminum-to-silicon contacts and thereby predicting the acceptability of the finished alloyed product. The subject method affords a determination immediately after metal deposition, and prior to the alloying step, while stripping of the metal and remetallization are still possible.